Grinding machine with feed rate changing device

ABSTRACT

A grinding machine comprising: a bed; a wheel slide slidably mounted on said bed; a grinding wheel rotatably mounted on said wheel slide; a work table for supporting a workpiece; feed means for moving said wheel slide toward and away from said workpiece; an electric power source; a first electrode mounted adjacent to said grinding wheel and connected to said electric power source for applying a potential to the surface of said grinding wheel; a second electrode mounted adjacent to said grinding wheel for detecting the change of the difference of potential caused by the approach of said grinding wheel to a workpiece in order to generate a control signal; an electrostatic screening member for encircling said second electrode except at the surface thereof opposed to said grinding wheel, said electrostatic screening member being connected to the ground; and control means for controlling said feed means so as to change the feed rate of said wheel slide in accordance with said control signal.

United States Patent Tomita et a1.

Oct. 7, 1975 GRINDING MACHINE WITH FEED RATE CHANGING DEVICE Inventors:Tamaki Tomita, Okazaki; Ryoji Yamada; Shiro Takayama, both of Kariya,all of Japan Toyoda Machine Works, LtdL,

Assignee:

Aichi-Pref., Japan Filed: Nov. 27, 1974 Appl. No.: 527,858

Foreign Application Priority Data Mar. 9,1974 Japan 49'27377 U.S. Cl51/165.77; 5l/165.92 Int. Cl. B24B 49/08 Field of Search 51/165 R,165.77, 165.87,

[56] References Cited UNITED STATES PATENTS 2,961,808 11/1960 Dungan51/165.92 3,090,171 5/1963 Stimson 51/165 R 3,172,240 3/1965Giardini..... 51/l65.92 X 3,550,327 12/1970 Kusakobe 51/l65.92

FOREIGN PATENTS OR APPLICATIONS 782,432 9/1957 United Kingdom 51/165.92

AMPLIFIER 1 OSCILLATOR REC T/F/ER ITE ME C/RCU/T CIRCUIT PrimaryExaminer-Harold D. Whitehead Attorney, Agent, or Firm-Oblon, Fisher,Spivak, McClelland & Maier [5 7] ABSTRACT A grinding machine comprising:a bed; a wheel slide slidably mounted on said bed; a grinding wheelrotatably mounted on said wheel slide; a work table for supporting aworkpiece; feed means for moving said wheel slide toward and away fromsaid workpiece; an electric power source; a first electrode mountedadjacent to said grinding wheel and connected to said electric powersource for applying a potential to the surface of said grinding wheel;.a second electrode mounted adjacent to said grinding wheel fordetecting the change of the difference of potential caused by theapproach of said grinding wheel to a workpiece in order to generate acontrol signal; an electrostatic screening member for encircling saidsecond electrode except at the surface thereof opposed to said grindingwheel, said electrostatic screening member being connected to theground; and control means for controlling said feed means so as tochange the feed rate of said wheel slide in accordance with said controlsignal.

4 Claims, 3 Drawing Figures GRINDING MACHINE WITH FEED RATE CHANGINGDEVICE BACKGROUND OF THE INVENTION 1. Field of the Invention Thisinvention relates generally to grinding apparatus, and more particularlyto a grinding machine provided with an apparatus for changing the feedrate of a grinding wheel relative to a workpiece just before thegrinding Wheel comes into contact with the workpiece.

2. Description of the Prior Art In recent years, there has beendeveloped a grinding machine provided with a feed rate changingapparatus wherein the outer periphery of a nonconductive grinding wheelis sprayed with a conductive coolant so as to place it in a conductivestate so that, when the grinding wheel comes into contact or approachesthe workpiece, an electrical connection may be formed between thegrinding wheel and the workpiece by the-conductive coolant. The feedrate changing apparatus is provided with a first electrode which ismounted adjacent to the grinding wheel for applying a potential to thesurface of the grinding wheel and a second electrode adjacent to thegrinding wheel for detecting the potential of the outer surface of thegrinding wheel through an electrostatic induction phenomenon causedtherebetween. Thus, the contact or approach of the grinding wheel withthe workpiece is detected on the basis of the change of the detectedpotential.

It was, however. difficult for such a second electrode to accuratelydetect in a stable manner the change of potential because of an inducedvoltage caused by induction and radiation from the environment.

SUMMARY OF THE INVENTION It is, therefore, an object of the presentinvention to provide a grinding machine provided with a new and improvedelectrode device incorporated in an apparatus for changing the feed rateof a grinding wheel just before the grinding wheel contacts theworkpiece.

It is another object of the present invention to provide a grindingmachine provided with a new and improved electrode device havingelectrostatic screening for accurately detecting in a stable manner theapproach of a grinding wheel to a workpiece.

Still another object of the present invention is to pro vide a grindingmachine provided with a new and improved electrode device wherein adetecting electrode is screened by an electrostatic screening member soas not to be affected by electrostatic induction from the environmentexcept at the surface of the grinding wheel opposed to the detectingelectrode.

The foregoing and other objects are attained in accordance with oneaspect of the present invention through the provision of a grindingmachine which comprises a bed, a wheel slide slidably mounted on thebed, a grinding wheel rotatably mounted on the wheel slide. a work tablefor supporting a workpiece, a feed device for moving the wheel slidetoward and away from the workpiece and other devices mentioned below. Afirst electrode is mounted adjacent to the grinding wheel and isconnected to an electric power source for applying a potential to thesurface of the grinding wheel. A second electrode is mounted adjacent tothe grinding wheel for detecting the change of the difference ofpotential caused in the approach of the grinding wheel to a workpiece inorder to generate a control signal. An electrostatic screening memberconnected to ground is mounted so as to encircle the second electrodeexcept at the surfact thereof opposed to the grinding wheel. A controldevice controls the feed device so as to change the feed rate of thewheel slide in accordance with the control signal.

BRIEF DESCRIPTION OFTHE DRAWINGS The foregoing and other objects of thepresent invention will be more fully appreciated as the same becomesbetter understood from the following detailed description of a preferredembodiment when considered in connection with the accompanying drawings,in which:

FIG. 1 is a schematic view showing apparatus for detecting the approachof a grinding wheel to a workpiece;

FIG. 2 is a longitudinal cross sectional view showing a second electrodedevice; and

FIG. 3 is a graph showing the relationship between the distance betweena grinding wheel anda workpiece and output voltage.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT Referring now to thedrawings, wherein like reference numerals designate identical orcorresponding parts throughout the several views, and more particularlyto FIG. 1 thereof, there is shown a work table 2 which is slidablymounted on a bed 1. The work table 2 fixedly mounts a head stock 3 and atail stock (not shown) for rotatably supporting a workpiece Wtherebetween. A wheel slide 4 is slidably mounted on the bed 1 so as tobe moved twoard. and away from the supported workpiece W. Theabove-mentioned grinding machine parts are made of conductive material.A nonconductive grinding wheel G such as, for example, a bitrifiedgrinding wheel is rotatably mounted on the wheel slide 4 through a wheelshaft 5.

A coolant nozzle 8 is secured on the top of a grinding wheel guard 12for discharging coolant downwardly to the grinding point or contactingposition of the grinding wheel G and the workpiece W during a grindingoperation. A pump Pc is connected to the coolant nozzle 8 by means of aconduit 9 for supplying coolant from a coolant reservoir (not shown) tothe coolant nozzle 8. A magnetic change-over valve is connected betweenthe coolant nozzle 8 and the pump Pc for opening and closing the conduit9. l

A feed cylinder 11 is mounted on the bed 1 for slidably receiving apiston and a piston rod 13 which is connected to the lower portion ofthe wheel slide 4. Fluid under pressure is applied to and is dischargedfrom the cylinder 11 through a magnetic change-over valve 14 forchanging the advance and the retraction of the wheel slide 4. Anotherchange-over valve 15 is used for changing the feed rate of the wheelslide 4. A check valve 16 is connected between the cylinder 11 and thechange-over valve 14 in parallel with the change-over valve 15 forpermitting the wheel slide 4 to rapidly retract.

There will not be described a feed rate changing device which changesthe feed rate of the wheel slide 4 or the grinding wheel G relative tothe workpiece W just before the grinding wheel G contacts the workpieceW or when the grinding wheel G makes initial contact with the workpieceW.

A first conductive nozzle which serves also as a first electrode deviceto provide the electric potential of the periphery of the grinding wheelG is insulatedly fixed to the wheel slide 4 for supplying a conductivecoolant to the periphery of the grinding wheel G in order to wet thegrinding wheel G. The first conductive nozzle 20 is connected to theconduit 9 through a relatively long nonconductive pipe 21 to prevent thecurrent applied thereto from leaking to the conductive coolant and inturn is connected to the pump Pc. A variable throttle 22 is interposedbetween the first conductive nozzle 20 and the conduit 9 for adjustingthe quantity of coolant applied to the grinding wheel G so that anappropriate coolant film may be formed on the outer peripheral edge ofthe grinding wheel G.

A second nozzle 24 for the supply of the conductive coolant isinsulatedly fixed to the side of the grinding wheel guard 12 and isopened adjacent to the clearance between the side of the grinding wheelG and a second electrode device 30. The second nozzle 24 is connected tothe pump Pc through a relatively long nonconductive pipe 25 and avariable throttle 26 is interposed between the pump Pc and the secondnozzle 24 for adjusting the quantity of coolant applied to the clearancebetween the side of the grinding wheel G and the second electrode device30.

An air nozzle 27 is fixed to the rear side of the coolant nozzle 8 andthe air-blowing opening thereof is opposed to the entire width of theouter peripheral edge of the grinding wheel G for discharging compressedair to prevent scatterring of the coolant.

The second electrode device 30 is mounted on the grinding wheel guard 12and is adjacent to the side surface of the grinding wheel grinding asshown in FIG. 2. A body 31 made of an insulating material is fixed tothe grinding wheel gaurd 12 so that the front end surface thereof 32 isopposed to the peripheral side surface of the grinding wheel G with asmall clearance therebetween of, for example, 0.5 millimeters. A secondelectrode 33 of a metallic disk is fixed to the bottom of a roundrecession 31a which is formed on the body 31 with a distance orthickness of l millimeter from the 'front end surface of the body 31. Anelectrostatic screening member 34 made of a metallic material of cupshape is received in and fixed to a circular slot 31/; whih is formed onthe body 31 so as to concentrically encircle the round recession 31a.Thus, the second electrode 33 is encircled by the electrostaticscreening member 34 except at its face which is opposed to the side ofthe grinding wheel G. A shielding wire 36 is connected to the body 31through a conventional connector 35. The shielding mesh conductor 36a ofthe shielding wire 36 is connected to ground at one end and is connectedat the other end to the electrostatic screening member 34 and isinsulated with respect to the second electrode 33. The second electrode33 is connected to the central conductor 36b of the shielding wire 36.The central conductor 36/; is connected to a control circuit describedhereinafter which controls the feed rate of the wheel slide 4 inaccordance with the approach of the grinding wheel G to the workpiece W.

A high frequency oscillator 40 is provided as an electric power sourceto apply a potential to the surface of the grinding wheel G. In thepresent embodiment, the oscillator 40 is designed so as to transmit ahigh frequency voltage of 10 Kilohertz aand 30 volts from one outputterminal thereof to the first conductive nozzle or first electrode 20.The other output terminal of oscillator 40 is connected to ground by bed1.

There will now be described the control circuit which detects thepotential of the peripheral surface of the grinding wheel G in order tocontrol the changing operations of the magnetic change-over valves 10,14 and 15.

An amplifier 41 is connected to the second electride 33 through thecentral conductor 36b of the shielding wire 36 for amplifying the inputvoltage applied thereto. The output terminal of the amplifier 41 isconnected to a high-pass filter circuit 42 which eliminates lowfrequency oscillations. In the present embodiment, the high pass filtercircuit 42 is designed so as to permit carrier voltage oscillations topass therethrough but to eliminate low frequency voltage fluctuationswhich are caused by drifts of electric circuit components and thefluctuation of commercial frequency (/60 Hertz). For example, if thefrequency of the carrier current is 10 Kilohertz, the high-pass filtercircuit 40 is designed to eliminate oscillations less than I Kilohertz.

A rectifier circuit 43 is connected to the output ter- I minal of thehigh-pass filter circuit 42 for rectifying and demodulating the carriercurrent transmitted there from. The output terminal of the rectifiercircuit 43 is connected to a low-pass filter circuit 44 which isdesigned to eliminate oscillations of more than 10 Hertz such aspulsating voltage fluctuations which are not eliminated by the high-passfilter circuit 42 or the rectifier circuit 43.

The output terminal of the low-pass filter circuit 44 is connected to amemory circuit 45 which memorizes an input voltage just prior to theadvance of the wheel slide 4 in accordance with a gate signal 45a whichis transmitted by a retraction-confirming limit switch (not shown) whenthe wheel slide 4 is in its retracted position. The output terminal ofthe memory circuit 45 is connected to a voltage-reducing circuit 46which reduces at a predetermined rate, for example /2, the outputvoltage of the memory circuit 45.

A comparator circuit 47 is connected at one input terminal to the outputterminal of the low-pass filter circuit 44 and at the other inputterminal to the output terminal of the voltage-reducing circuit 46.Thus, the comparator circuit 47 generates a feed rate changing signalwhen the output voltage of the low-pass filter circuit 44 is less thanthat of the voltage-reducing circuit 46. The output terminal of thecomparator circuit 47 is connected to a relay circuit 48 which energizesthe solenoides of the magnetic change-over valves 10 and 15 when thefeed rate changing signal is generated by the comparator circuit 47. j

The operation of the aforementioned preferred embodiment will now bedescribed.

FIG. 1 shows the position prior to the grinding operation in which thewheel slide 4 and the other accompanying parts are in their initialpositions or states. When an operation-starting signal is applied to therelay circuit 48, the pump Pc is driven to supply coolant to the firstconductive nozzle 20 and the second nozzle 24. In addition, a pump P andan air pump (not shown) are driven to supply operational pressure fluidand compressed air, respectively. The coolant discharged from the firstnozzle 20 and the second nozzle 24 is directed to the outer peripheraledge of the grinding wheel G and to the side surface of the grindingwheel G through the clearance between the grinding wheel G and thesecond electrode device 30.

The grinding wheel G starts to rotate in a counterclockwise direction inFIG. 1 in accordance with a start signal and is wetted by the coolantdischarged from the first conductive nozzle 20. The variable throttle 22is adjusted prior to the machining cycle so that the coolant is directedto the outer peripheral edge of the grinding wheel G withoutinterruption and wets only the outer peripheral edge of the grindingwheel under the centrifugal force caused by the rotation of the grindingwheel G. The variable throttle 26 is adjusted so that the coolantsupplied by the second nozzle 24 wets the side surface of the grindingwheel G radially outward beyond the electrode device 30 under thecentrifugal force and does not wet in the vicinity of the wheel shaft 5of the grinding wheel G. Thus, a conductive surface is formed by theconductive coolant on the outer peripheral edge and the outer peripheralside of the grinding wheel G which is maintained in nonconductiverelationship with the wheel shaft 5.

The carrier oscillator 40 is then operated to transmit the carrier, forexample, a kilokertz frequency at 30 volts. This voltage is applied tothe periphery of the grinding wheel G through the coolant dischargedfrom the nozzle so that a predetermined potential is given to theperiphery of the grinding wheel G. A voltage which corresponds to thepotential on the periphery of the grinding wheel G is caused by anelectrostatic conduction phenomenon at the second electrode 33 and isdirected to the input of the amplifier 41 through the shielding wire 36.

A relationship between the output voltage V of the low-pass filtercircuit 44 and a distance S between the grinding wheel G and theworkpiece W is shown in FIG. 3 wherein the output voltage V is V1 whenthe distance 5 is larger than a distance a and the output voltage Vdecreases because of the reduction of the potential on the periphery ofthe grinding wheel G as the grinding wheel G approaches the workpiece Wwithin the distance a. The output voltage V attains V2 when the distanceS is zero or when the grinding wheel G contacts the workpiece W.

Experimental data for the present invention was as follows when thedistance a 0.3 millimeters Vl 2 volts and V2 0.7 volts When the wheelslide 4 starts to advance toward the workpiece W away from its retractedor initial position by the change-over of the valve 14 to the port (1)thereof, the gate signal 45a which is directed to the input of thememory circuit 45 is interrupted. The memory circuit 45 memorizes thevoltage V2 just before the stoppage of the gate signal 45a and continuesto transmit the voltage V2 until the wheel slide 4 returns to itsretracted position. The voltage-reducing circuit 46 generates areference voltage V0 which is reduced at a predetermined rate (forexample, V0 V2/2).

' As the grinding wheel G approaches the workpiece W during the advanceof the wheel slide 4, the output voltage V of the low pass filtercircuit 44 decreases as shown in F IG. 3. When the output voltage Vattains the reference voltage V0 of the voltage-reducing circuit 46 orwhen the distance S between the grinding wheel G and the workpiece W isequal to b, the feed rate changing signal is generated by the comparatorcircuit 47. The magnetic change-over valve 15 is changed to its port(l)in accordance with the feed rate changing signal to thereby change thefeed rateof the wheel slide 4 from a rapid feed rate to a slow orgrinding feed rate defined by a throttle contained in the valve 15. Atthe same time, the magnetic change-over valve 10 is changed to its. port(I) to thereby permit a large supply of coolant to be supplied from thecoolant nozzle 8 to the grinding point. Thus, the grinding wheel Gstarts to grind the workpiece W.

In case the second electrode 33 is not provided with the electrostaticscreening member 34, induced voltages due to radiation and induction ofnear electrical parts and transmission lines appear at the secondelectrode 33. For example, such an induction occurs in the changingoperation of magnetic change-over valves or in the switching operationof contacts. An induced voltage having a frequency near the carrierfrequency of the carrier ocillator 40 is not eliminated even by thehigh-pass filter circuit 42 and the low-pass filter circuit 44. Theoccurrence of such an. induced voltage disturbs the relationship betweenthe output voltage V of the low-pass filter circuit 44 and the distanceS between the grinding wheel G and the workpiece W. Therefore, theposition where the feed rate of the wheel slide 4 is changed from therapid to the slow is not maintained constant.

Since the second electrode device 33 according to the present inventionis provided with the electrostatic screening member 34 encircling thesecond electrode 33, no induced voltage clue to radiation and inductionof other electrical parts and transmission lines except the grindingwheel G occur with the result that the detected distance between thegrinding wheel and the workpiece W is maintained stable.

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is to beunderstood therefore that within the scope of the appended claims theinvention may be practiced otherwise than as specifically describedherein.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:

l. A grinding machine comprising:

a bed;

a wheel slide slidably mounted on said bed;

a grinding wheel rotatably mounted on side wheel slide;

a work table for supporting .a workpiece;

feed means for moving said wheel slide toward and away from saidworkpiece;

an electric power source;

a first electrode mounted adjacent to said grinding wheel and connectedto said electric power source for applying a potential to the surface ofsaid grinding wheel;

a second electrode mounted adjacent to said grinding wheel for detectingthe change of the difference of potential caused by the approach of saidgrinding wheel to a workpiece in order to generate a control signal;

an electrostatic screening member for encircling said second electrodeexcept at. the surface thereof opposed to said grinding wheel, saidelectrostatic screening member being connected to the ground; and

said first electrode is a conductive nozzle for supplying a conductivecoolant to the periphery of said grinding wheel.

4. A grinding machine acording to claim 1 further comprising a coolantnozzle for supplying a conductive coolant to the clearance between saidgrinding wheel and said second electrode.

* l l= =l

1. A grinding machine comprising: a bed; a wheel slide slidably mountedon said bed; a grinding wheel rotatably mounted on side wheel slide; awork table for supporting a workpiece; feed means for moving said wheelslide toward and away from said workpiece; an electric power source; afirst electrode mounted adjacent to said grinding wheel and connected tosaid electric power source for applying a potential to the surface ofsaid grinding wheel; a second electrode mounted adjacent to saidgrinding wheel for detecting the change of the difference of potentialcaused by the approach of said grinding wheel to a workpiece in order togenerate a control signal; an electrostatic screening member forencircling said second electrode except at the surface thereof opposedto said grinding wheel, said electrostatic screening member beingconnected to the ground; and control means for controlling said feedmeans so as to change the feed rate of said wheel slide in accordancewith said control signal.
 2. A grinding machine according to claim 1further comprising a body made of an insulating material and having acircular slot for receiving said electrostatic screening member and around recession encircled by said circular slot for receiving saidsecond electrode.
 3. A grinding machine according to claim 1 whereinsaid first electrode is a conductive nozzle for supplying a conductivecoolant to the periphery of said grinding wheel.
 4. A grinding machineacording to claim 1 further comprising a coolant nozzle for supplying aconductive coolant to the clearance between said grinding wheel and saidsecond electrode.